EP1941091B1 - Colorimetric device for relative colour measurement of a material web - Google Patents

Abstract

A device is disclosed for relative colour measurement of a moving material web using a multirange colour sensor for determining and comparing colour degradation of zones which extend parallel to the material web length. In order to exclude ageing effects of the lighting necessarily required for colour measurement, as well as errors due to the ambient light and parasitic effects caused by different temperatures and mechanical errors, a colour sensor (17) is provided having a plurality of measurement points (11 to 13) which are moved together transversely to the length of the material web and have a common light source (22).

Description

The invention relates to a device for relative color measurement on a moving material web with the aid of a multigrade color sensor, in particular tristimulus color sensor, for determining and comparing the color loss in areas extending parallel to the material web length.

So-called color sensors are described in WO97 / 17604A and WO96 / 09533A , However, these are not sensors for determining the color itself but for detecting the color intensity. The known sensors, for example, red and blue - with the same intensity - not distinguish. In EP0675466A2 For example, a color line camera for determining the surface finish of objects will be described. A color line camera is not a generic multirange color sensor. DE4238234A1 relates to a process for the dye liquor distribution on a textile web, in which the brightness of the still wet web dipped in the ink is used as a parameter for the color distribution alone.

In installations in which wide material webs are to be monitored with regard to their color properties, textile fabric webs especially in the case of uni-colorations, it is important that the current color over the entire web width and length be the same. Such systems can be found, for example, in the textile industry but also in papermaking and finishing, in the production of plastic floor coverings, veneers, etc. In this case, material web widths of several meters may occur. The material webs are in the production process often moved at high speeds (in the web longitudinal direction), often several meters of goods per second are promoted.

Color errors are often specified in CIELab system as the color error dE value. The following are preceded by this: The filter functions defined in the CIE 1931 CMF form the basis for many of today's common color models. There are so many color models because different requirements can not be met with the same model. One such requirement is often to describe color errors. For this purpose, adapted to the human visual perception, the so-called CIELab model was developed. The associated Lab values formed in relation to a reference result directly from the CIE 1931 CMF. From these Lab values, in turn, the aforementioned color error dE can be calculated.

It is generally accepted that a dE of "1" is no longer perceived by most people. However, practice shows that even this color model or the "dE = 1 rule" does not sufficiently represent human color perception with regard to color differences in all color ranges. It can be assumed that trained eyes (for example a staining master in textile finishing) also recognize chromatic aberrations of dE = 0.3. The result for systems described above is the requirement for a color measuring system with which errors of dE <= 0.1 can still be reliably resolved. With this order of magnitude of the measuring accuracy, parasitic effects due to temperature, mechanical measuring errors (eg unequal distances at the measuring points), ambient light and above all due to aging of the luminaires which are absolutely necessary for the color measurement can no longer be ignored.

For carrying out the abovementioned color measurements, there are, for example, so-called three-area color sensor elements. A tri-area color sensor is a single sensor element that divides incoming light of any wavelength into three wavelength ranges and provides separate information for each area. If this sensor operates in the visible range of light and in addition the three wavelength ranges have sensitivity curves, the at least traceable to the CIE 1931 CMF, this is called a true color sensor.

Three-range color sensors typically work as stand-alone devices, which are characterized by the fact that the light source is integrated into the devices or controlled by them individually. Since such a device is a self-contained unit, aging effects of the light source affect each device and thus each measuring point individually. Even 'if during commissioning of a system, the individual measuring points were compensated relatively well by a suitable adjustment, the measurement results run apart again after a short time because of the different aging effects of the individual lights or light sources, so that a new adjustment is necessary. At the latest, if after a longer period of operation of one of the devices, eg. B. because of a defect, must be replaced, a readjustment is mandatory.

However, problems may also arise from the three-range color sensor device itself, for example when the devices result from the filter characteristics implemented in accordance with the respective region. If these filter characteristics have steep edges in the transition to the stopband and / or flat "roofs" in the passband, then there are zones on the sidewalls in the visible spectrum of light where slightest changes in color result in extreme changes in the measurement result, while at the same time in other colors Even larger color errors in the measurement result are hardly clear. Since filter functions can not be reproduced with any accuracy, especially for filters with steep flanks, the additional problem arises that different sensor elements of the same type due to production tolerances in the filters with high probability under the same measurement conditions provide different measurement results. This is especially true if the color to be measured has appreciable spectral components in the region of the filter edges. Such tristimulus color sensor devices are therefore rather unsuitable for the stated measurement task.

Therefore, there are the aforementioned three-range color sensor devices with "true-color" properties. In this case, the filter functions of the so-called color matching function CIE 1931-2 ° of the standard observer are modeled. It can be said simply that if a sensor realizes the filter functions described in this standard, it is possible to directly derive measured values which describe the human color perception "best", since the human eye also works in principle in a three-region method. Although the filter functions described in the standard are often incorrectly referred to as eye sensitivity curves, they are directly derived from empirical experiments on human vision.

The described filter function offers not only the advantage of "soft" filter curves, which therefore also tolerate more production differences, but in this special case also the possibility to use the measured values with a much higher accuracy for a rating in the CIELab system or the color differences arise in principle only from the accuracy of the sequential system, which further processes the analog signals of the sensor device.

Because of the aforementioned problems that arise when individual commercially available color sensors are used at several measuring points, the aforementioned measurement task is so far solved in a conventional manner. This comes after DE 43 08 501 A1 . EP 0411 414 B1 and EP 1276 926 B1 a single colorimeter is used, which - mounted on a traversing shaft - continuously in the direction of the web width is moved back and forth and doing at individual measuring points individual measurements. These results can then be compared. Due to the required resolution, a spectrometer system is used as the colorimeter. The advantage of this arrangement is that many of the above-mentioned parasitic effects and thus especially the aging of the light source required here affect the same effect only on a single device and thus on all measuring points. Influence such effects so the relative accuracy is not. In addition, the use of a spectrometer in principle allows a high resolution in the color measurement.

However, the latter conventional method also has serious disadvantages. The spectrometer system itself, but also the required axle system for traversing the measuring device, are expensive. Since the axis system and the measuring system are constantly moving, the device is subject to high mechanical wear. Furthermore, the measuring times, in the spectrometer strongly depend on the intensity of the incident light. To keep the measuring time short, very bright light sources are used, which are also expensive and have a limited life. Since these devices are generally not to be modulated at higher frequencies, differ Differenzmeßverfahren so that a significant sensitivity to the ambient light is to be accepted. Finally, it follows from the time for the movement (of the individual measuring device) transversely to the fabric longitudinal direction and from the relatively long individual measuring times that - especially at higher web transport speeds - several meters of goods have passed through before there are sufficient measurements for a color profile in the transverse direction.

The invention is based on the object to provide a device by means of which it is possible to significantly reduce the total cost of Farbmeßsystems at increased measuring speed, without sacrificing a relatively high accuracy and sensitivity and an acceptable life. Aging effects should not lead to different measurement results at the individual measuring points. Ambient light errors should be compensable.

For the aforementioned device for relative color measurement on a passing material web by means of a multi-area color sensor, the solution according to the invention is specified in claim 1. Some improvements and Further embodiments of the invention are described in the subclaims.

According to the invention, the color sensor has a plurality of measuring points running concurrently transversely to the material web length with a, preferably single, common light source. "Synchronous" means that the web is simultaneously scanned at two or more measuring points. Above all, the synchronization of the measuring points overcomes the deficiencies of the conventional CIELab system. Therefore, high demands are made in the context of the invention, especially with respect to the synchronization of the measuring points. The material web to be tested may preferably be a textile fabric web on the one hand or a paper or plastic web, a veneer tape or the like elongate non-textile fabric on the other hand.

The color measuring device according to the invention is equipped with a multi-range color sensor device or element with synchronization of the measuring points of the sensor. Because of the above-mentioned problems with simple three- or multi-range color sensor devices, true-color three- or multi-range color sensors are preferably used within the scope of the invention. The measuring points are assigned a common light source. If necessary, a temperature compensation of the color sensor devices can be provided. In this way, the invention provides the possibility to record measured values from different measuring points at the same time, without aging phenomena of the light source can cause errors, because aging processes of the light source on all - according to the invention concurrently - measuring points or interrogation evenly.

According to the invention, a temperature compensation of the device is provided to compensate for corresponding drift phenomena. Thus, if there is a risk that the temperature at the positions of the individual measuring instruments or measuring points is different, such a temperature compensation may be advantageous. Falsifications of the measurement results by temperature changes can be made in the usual way in the technical field.

According to another aspect of the invention, it becomes possible to compensate for errors caused by extraneous light or ambient light. For this purpose, a difference measurement, once with the lights on and once with the lighting off, made.

Finally, the invention generally relates to a device for relative color measurement with the aid of a true color multirange color sensor. In general, however, a tristimulus color sensor is sufficient. Preferably, the device according to the invention is equipped with true color tristimulus color sensor devices. Optionally, a high accuracy, synchronous color measurement is obtained on multiple true color type three-range color sensor elements at multiple tracking points. The above-mentioned problems with the filter characteristics can be satisfactorily managed by a target-related linear and / or non-linear correction matrix for matching the filter function of each of the individual measurement points.

Fig. 1

einen Foulard mit anschließender Quetsche; und

Fig. 2

das Schema einer erfindungsgemäßen Vorrichtung zur Farbmessung an der nach Fig. 1 behandelten Warenbahn.

Details of the invention will be explained with reference to the schematic representation of an exemplary embodiment relating to a textile material web, for example. Show it

Fig. 1

a foulard with a subsequent squeeze; and

Fig. 2

the scheme of a device according to the invention for color measurement at the after Fig. 1 treated web.

In the embodiment according to Fig. 1 is a textile web 1 in the extended state by a generally designated 2 padder, z. B. via rollers 3 and 4, in a treatment liquid 5, z. As color, dipped and then brought in one of two (in the arrow direction) against each other to be pressed rolls pinch 6 to a predetermined residual moisture. In the squeezer 6 is a set to the same width and length of the web 1 residual moisture become. In order to check whether the goal of a uniform distribution of the treatment liquid in the web 1 is reached, the web is passed over a roller 7, which is associated with a sensor device 8 according to the invention, in the arrow direction. The sensor device 8 with roller 7 and web 1 is in Fig. 2 shown with some essential details (in a plane with the axis 9 of the roller 7).

In the embodiment according to Fig. 2 the web 1 running through the roller 7 are assigned three detectors 11, 12 and 13. (11 = detector left, 12 = detector center, 13 = detector right). The detectors 11 to 13 are fixed at a predetermined distance a from the surface of the web 1 or the surface of the roller 7 or reciprocated in compliance with the distance a transversely to the web transport direction. The detectors 11 to 13 are connected via optical fibers 14 to 16 with the channels A to C of a color sensor 17. The color sensor 17 has a power supply 18 and a terminal 19 to a PC 20 (controller or host). The PC 20 is switched to a line control 21, which detects the squish force distribution in the squeezer 6 Fig. 1 so controls that the desired uniform distribution of residual moisture in the web 1 is constantly maintained or set.

An essential feature in the context of the present invention is that the color sensor 17 more, z. B. has three, transversely to the web length co-rotating measuring points (detectors 11 to 13) with a common light source. In Fig. 2 the common light source or illumination is designated 22. The lighting has a control connection 23 to the color sensor 17 and light guides 24 to 26 to the individual detectors 11 to 13.

LIST OF REFERENCE NUMBERS

1 =

web

2 =

Foulard

3, 4 =

roll

5 =

treatment liquid

6 =

Quetsche

7 =

roller

8 =

sensor device

9 =

axis

11 to 13 =

detectors

14 to 16 =

optical fiber

17 =

Color sensor

18 =

power supply

19 =

connecting cable

20 =

PC

21 =

line control

22 =

lighting

23 =

control connections

24 to 26 =

optical fiber

a =

distance

A to C =

channels

Claims (4)

1. Device for measuring the relative coloration of a moving material sheet (1) by means of a multirange colour sensor (17), in particular a three-range colour sensor, for determining and comparing deficiencies in colour on areas of material sheets extending parallel to the length of the material sheet, characterized in that a true-colour sensor (17) with temperature compensation and means for performing differential measurements with switched on and switched off lighting (22) are provided, and in that the colour sensor (17) has several measurement points (11 to 13) to be moved at right angles to the length of the material sheet with a common light source (22) for simultaneously scanning the material sheet (1).
2. Device according to claim 1, characterized in that a target-related linear and/or non-linear correction matrix is provided for matching the filter function of each individual measurement point (11 to 13).
3. Device according to claim 1 or 2, characterized in that the material sheet (1) is a textile material sheet.
4. Device according to claim 1 or 2, characterized in that the material sheet (1) is a paper or plastic sheet, a veneer strip or similar elongated non-textile type of surface.

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